Re: Join Advice and Assistance

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От Stephen Belcher
Тема Re: Join Advice and Assistance
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Msg-id b4651e821002220915w13f81ed4p26fb0a7126ce1fff@mail.gmail.com
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Ответ на Re: Join Advice and Assistance  (Rob Sargent <robjsargent@gmail.com>)
Ответы Re: Join Advice and Assistance  (Gary Chambers <gwchamb@gmail.com>)
Список pgsql-sql
To expand on Rob's reply:

If you want to return a single row for each user, regardless of the number of email addresses, you might use ARRAY() with a subquery, eg (haven't tested this to make sure it completely works):

SELECT u.*, um.*, ARRAY(SELECT emailaddr FROM user_emailaddrs em WHERE em.userid = u.userid AND em.is_active) AS email_addresses
FROM users u INNER JOIN usermetas um ON u.userid = um.userid;

Of course, this will return the addresses as a character varying[], with output like {user@domain.tld,user@domain.tld}, and would require some minor contortions to present it to users cleanly. The array_to_string function may help you make it easier to display the results.


Hope this helps,
--Stephen Belcher

On Mon, Feb 22, 2010 at 12:05 PM, Rob Sargent <robjsargent@gmail.com> wrote:
My mistake.  Should answer these things late at night.

I think you will find that arrays will be your friend[s]


On 02/22/2010 08:51 AM, Gary Chambers wrote:
Rob,

Thanks for the reply...

If you want records for user without email addresses you will need an outer
join on user_emailaddrs

/* untested */
select u.userId, u.lname, u.lastname ,m.startdate, a.emailaddr
from users u
join usermetas m on u.userid = m.userid
left join user_emailaddrs a on m.userid = a.userid

My question was related more toward eliminating the query returning a
record for each record in the one-to-many table.  I see now that I'm
going to have to aggregate the e-mail addresses in order to return a
single row.  Thanks again.

-- Gary Chambers

/* Nothing fancy and nothing Microsoft! */

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